DRI
DRI stands for direct reduced iron, also known as sponge iron. It is a solid product of directly reduced iron ore in form of pellets/fines/lumps. Direct reduction of iron ore involves removal of oxygen from iron ore using non coking coal or reformed natural gas as reducing agent without melting. Different processes for direct reduction falls in two categories as shown.
Advantages for direct reduction processes
- It reduces burden on high grade metallurgical coke.
- These processes utilise iron ore fines hence decrease cost of production.
- With increased efficiency in steel making processes, production of scrap needed during steel making has decreased and DRI is a very good replacement of scrap.
- The process is environment friendly and one of the sources of producing green steel.
- High temperature for melting is not required, saving energy needed to reach such high temperature.
- Easier process control and lower capital investment as compared to blast furnace.
PROPERTIES OF SPONGE IRON
- Apparent density of sponge iron varies between 1.5 – 4 g/cm3 and bulk density varies between 1.5 -1.9 t/m3.
- Specific surface area of DRI varies between 0.5 – 4 m2/g.
- Carbon content varies between 0.1- 0.15 for coal based and up to 2.5% for gas based DRI.
- Sponge iron is highly porous due to removal of oxygen from the lumps of iron ore.
- High porosity and large surface area make sponge iron prone to reoxidation, if heated to ignition temperature of 200℃ or when comes in contact with moisture at normal temperature.
- Sulphur content of gas based DRI is low provided sulphur content of oxide feed is also low.
- Tramp elements such as zinc, arsenic, tin, copper, lead etc. are not found in DRI.
- During direct reduction process, only oxygen gets removed from iron ore feed, gangue material composition remains the same. If proper composition of raw materials is used, DRI can have uniform chemical composition with narrow range of variation.
- DRI have high content of FeO, which sometimes proves to be advantageous as formation of CO from residual oxygen of FeO takes place which helps in stirring of the hot bath during steel making.
After production of DRI, it is used in electric arc furnace where it melts to produce steel. This alternative route of iron making is very much needed in today’s world. As in today’s world we must take immediate actions to protect climate and hence our mother Earth. At the same time, we cannot reduce our dependence on iron and steel so an approach is needed which serves both purposes.
With some improvement in Direct reduction processes, like use of green hydrogen as reducing agent in DRI technology or using green hydrogen in tuyeres of blast furnace as replacement of PCI(Pulverised coal injection) can meet the above mention purpose. Along with this electricity needed in electric arc furnace, needs to be produced from renewable energy sources to meet low carbon economy.
India has already started working on formulating a green steel policy and is exploring the process of having its own pure hydrogen based DRI plant.
